Pick-and-place machines are commonly used in automated semiconductor equipment to accurately deliver components or materials onto semiconductor substrates, such as leadframes. An example is the die bonding machine, which transfers cut wafer dice or chips from a wafer table onto a substrate in a “pick-and-place” operation. For operational simplicity, single bond head systems are normally used to perform the pick-and-place operation. However, there is a limitation in the throughput (normally quantified in Units Per Hour or “UPH”) attainable for single-head systems. Present systems with single bond heads cannot sufficiently fulfill the increasing demand for high throughput, and therefore there is a desire to develop systems with multiple bond heads that can perform die-bonding simultaneously.
In U.S. Pat. No. 5,397,423 for “Multi-head Die Bonding System”, multiple bond heads are spaced apart and mounted on a single conveyor mechanism. The bond heads pick up semiconductor dice from a wafer table and bond the dice to a substrate at a separate station. Although throughput from such a multi-head system is higher than for single-head systems, the arrangement of heads in this design is constrained by the configuration of the substrate. This system is not sufficiently flexible. The space available to accommodate the multiple bond heads and conveyor system is another problem.
There are mainly two other types of prior art multiple bond-head systems. They are cascade line systems as shown in FIG. 1 and multiple bond-arm systems as shown in FIG. 2. The bonding methods and apparatus for such systems will be described below.
As shown in FIG. 1, a cascade line system is constructed by linking two individual bonding machines 101, 102 for bonding dice to substrates 103 at a pair of bonding locations 104, 105. The minimal configuration of this system should include at least two die delivery devices 106, 107, two die supplying devices 108, 109, two pick optical systems and two bond optical systems (not shown). Die delivery devices 106, 107 pick up dice from their corresponding wafer table 108, 109 and transfer them to the bonding locations 104, 105 of the substrate 103 where the dice are bonded. A substrate conveying device 110 is provided to act as a connection between the two bonding machines 101, 102, for conveying substrates from an offload section of one machine 101 to the onload section of the other machine 102.
For cascade line systems as shown in FIG. 1, a malfunction of an individual machine 101, 102 will affect the overall machine performance. Moreover, since the machine is more complex with a higher number of devices, there is a higher possibility of failure.
As shown in FIGS. 2a and 2b, a multiple bond-arm system comprises a substrate conveying device 201, two die supplying devices 202, two pick optical systems (not shown), one bond optical system (not shown), a die delivery device 203 and two bond arms 204. The bond arms 204 can be mounted either in a pair on a linear carriage as shown in FIG. 2a or in a V-shaped layout on a rotary platform as shown in FIG. 2b. For both system configurations, the two die supplying devices 202 are mounted on opposite sides of a substrate-conveying device 201. The relative positions of the bond arms 204 are arranged such that the pick-and-place motions can be performed simultaneously by using a common die delivery device 203.
For systems with multiple bond arms, in which each bond arm carries a bond head that is mounted on a single die delivery device either on a linear arm or on rotary V-shaped arms as shown in FIG. 2a and FIG. 2b, the bond heads are coupled together so that their positions are mutually dependent. The simultaneous pick-and-place motion is only possible when locations of both bond heads are precisely aligned with the pick and bond points. If there is an error in aligning the positions as well as the level adjustments for each individual bond head during machine operation, the die delivery device 203 will be unable to make any compensation for the positional error of the individual bond heads as well as for dimensional deviations among the die and substrate.
Further, large footprints are required for both the cascade line and multi-arm systems since more space is required to accommodate the duplicated devices in the form of extra wafer tables and optical tables. A high apparatus cost for both cascade line and multi-head systems is thereby incurred.